1. Field of the Invention
The present invention relates to an apparatus and method for fabricating a liquid crystal display device, and more particularly, to an apparatus for forming an alignment layer and an auto-calibration method thereof for a liquid crystal display device.
2. Discussion of the Related Art
In general, a liquid crystal display device uses optical anisotropy and polarization properties of liquid crystal molecules to produce an image. For instance, the orientation of the liquid crystal molecules can be aligned in a specific direction controlled by an applied electric field. As the applied electric field changes, so does the alignment of the liquid crystal molecules. Due to the optical anisotropy of the liquid crystal, the refraction of incident light on the liquid crystal molecules also changes depending on the alignment direction of the liquid crystal molecules. Thus, by properly controlling an electric field applied to a group of liquid crystal molecules in respective pixels of a liquid crystal display device, a desired image can be produced by diffracting light.
The liquid crystal display device generally includes a first substrate, a second substrate and a liquid crystal layer interposed between the first and second substrates. A spacer is also interposed between the first and substrates to maintain a predetermined space between the substrates, and a sealant is used to bond the substrates to each other at the edges of the substrates.
In general, a method for fabricating a liquid crystal display device includes coating an alignment layer on a substrate, rubbing the alignment layer and then forming a spacer on the substrate. Further, a sealant is printed at edges of the substrate with an opening as a liquid crystal injection opening. After aligning the substrate with a second substrate, the substrates are sealed by the sealant with a predetermined space therebetween. Then, liquid crystal is injected into the predetermined space between the substrates through the opening, thereby forming a liquid crystal cell.
Typical methods of coating an alignment layer include screen-printing method, photolithography method, and inkjet-printing method. Although the screen-printing method is a relatively simple and low-cost method, it is not suitable for making a high-density model, because alignment layer formed by the screen-printing method has poor uniformity of depth and width. In comparison, the photolithography method produces alignment layers with good uniformity, but the photolithography method is a more complicated method using expensive apparatus and suffers frequent damages, thereby increasing material cost. Further in comparison, the inkjet-printing method has been the subject of recent research and development because of its wide applications and low-cost.
FIG. 1 is a schematic view of an inkjet type apparatus for coating an alignment layer according to the related art. In FIG. 1, a tilt controllable inkjet head 3 supported by a head support 4 is placed above the horizontal printing stage 2 on which a substrate 1 is disposed. The substrate 1 on the printing stage 2 can be fixed or movable and the number of the inkjet head 3 can be determined based on size of the printing stage 2. The inkjet head 3 sprays an alignment material onto the substrate 1 via a spray hole (not shown), while the head support 4 and the printing stage 2 are moved by a loading means, such as a rail. For example, the head support 4 and the printing stage 2 are moved in a manner such that rows of the alignment material are sprayed sequentially onto the substrate 1 via the spray hole, thereby forming an alignment layer on the substrate 1.
FIG. 2 is a cross-sectional view of an apparatus for measuring a pitch between ink according to the related art. In FIG. 2, after an alignment material is formed on a substrate, the substrate is moved into an apparatus 20 for measuring a pitch between the alignment material. Because such a pitch determines the quality of the alignment layer and the substrate, a substrate having a unsatisfactory pitch can be detected and discarded as a test substrate. In particular, the measuring apparatus 20 includes a microscope 21 for measuring a distance D between the rows of the alignment material formed on the substrate, thereby detecting any abnormal pitch of the alignment material based on the measured distance. However, such a measurement by another apparatus increases production time, reduces efficiency and requires larger work space, even though the pitch of the inkjet head 3 shown in FIG. 1 and its spray hole affect the pitch of the alignment material.